Kitchen sink leaking to outside wall

I have a strange plumbing problem, was searching the internet for a clue and found this forum. It looked like a nice bunch of folks so I registered.

Here's my problem. My house is about 25 years old. The sink is a porcelain, double basket, with a waste disposal under the left side, and a dishwasher connection.

Earlier today my wife was washing dishes; she had the stopper in the right side, full of water, and the faucet running into the left side for rinsing. After she let the water out of the right side she walked out onto the concrete patio and there was a water puddle on the concrete. The outside wall is stucco, and right down near the concrete there is a little hole where I can just barely see the down pipe from the sink drain.

After coming home from work I was able to recreate the problem by filling the right side with water, run the faucet into the left side, then release the right side into the drain. Then, through the little outside hole, I could see water dripping down from inside the wall. It's not coming from the pipe, at least not in the area of the hole.

What I'm wondering is, do you think I might have one of these in the wall, and the water is backing up into the down pipe and coming up out of the Air Vent? I can see this happening if the drain is partially clogged.

I checked all of the plumbing under the sink, it's all dry. I can't think of anything else.

Oh, and by the way, all of the pipes (except for the down pipe from the right sink basket) are PVC.

Anybody have an idea what's going on? I can supply pictures, if that would help, just let me know.

If it's an AAV it should only allow air in and seal itself afterwards. Although they fail quite readily and that is probably why they come threaded! Of course it should not be installed in a wall or any concealed location but hard to tell without actually being there.

A pipe transition is a more likely culprit with an elastomeric gasket joining the two. If it slipped off then the two pipes (PVC to glavanized, etc) would no longer be sealed allowing waste to flow through but rather out.

The line may have a nail or screw in it to, its hard to say, or a joint that wasnt glued or was but is leaking. They sell a scope camera that you can drill a small hole in the wall and take a look inside but they are expensive and you will probably need to call a plumber to locate the leak or tear the wall open so you can see where its coming from

the line may have a nail or screw in it to, its hard to say, or a joint that wasnt glued or was but is leaking. They sell a scope camera that you can drill a small hole in the wall and take a look inside but they are expensive and you will probably need to call a plumber to locate the leak or tear the wall open so you can see where its coming from

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see the above post;
there was also a time in calif, when there was a problem with a b s plastic sewer pipe
but more then likely it's just a screw in pipe, like when you get one in a tire but it does'nt go flat right away, it just taken time for the nail or screw to rust out ! !
But it only shows up when you run lots of water though pipe puts water out

take a hammer and bust out the stucco around the leak !
Make a good size hole to expose at least a couple of feet of pipe then take pictures of area and post here then we can tell you how to fix pipe then
i will tell you how to fix the stucco

Okay, here's a new twist to the story. The bottom of the cabinet under the sink is very damp. It's been wet before, but before I always had found plumbing leaks under the sink baskets. But this time, no leaks under the sink. So, I'm thinking that water from the leak in the wall is getting into the cabinet somehow. So, today I'm going to rip out the cabinet bottom. It needs to be replaced anyway. I'm going to do all I can to not rip a hole in the stucco, if at all possible.

Okay, here's what I found. The joint right above the clean out plug is leaking, and the joint right above it is leaking on the other side, on the stucco side of the joint (the third photo). I can feel wetness back there with my fingers. Here's some photos:

How hard is this to repair? It looks like a bigger job than I'm willing to tackle.

cutting that out and replacing it isnt a big deal but it is abs so you either need to replace it with abs or use ferncos and pvc. If you dont feel comfortable call a plumber and make sure its done right.

It looks like there is glue on/in the joint. What's weird is, while running water down the drain and watching the joint, water just seeps right out through the glue! This pipe is only about a half inch from the outside wall. Where I live the temperature right on the outside of that wall gets up to 110 in the summer, and freezes in the winter. I'm guessing that the constant heat and cold over the last 25 years has taken it's toll.